1) The copy assignment operator is protected, and is deleted. Output streams are not CopyAssignable.

2) The move assignment operator exchanges all data members of the base class, except for rdbuf(), with rhs, as if by calling swap(*rhs). This move assignment operator is protected: it is only called by the move assignment operators of the derived movable output stream classes std::basic_ofstream and std::basic_ostringstream, which know how to correctly move-assign the associated streambuffers.